Spinflop transition in dopped antiferromagnets

Abstract

In this paper we compute the mean field phase diagram of a doped antiferromagnet, in a magnetic field and with anisotropic exchange. We show that at zero temperature there is a metamagnetic transition from the antiferromagnetic configuration along the z direction to a spin-flop state. In the spin flop phase the system prefers a commensurate magnetic order, at low doping, whereas at larger doping the incommensurate phase is favorable. Contrary to the pure Heisenberg case, the spin flop region does not span an infinite area in the ('Delta',h) plane, where 'Delta' is the exchange anisotropy and h is the external magnetic field. We characterize the magnetic and charge-transport properties of the spin-flop phase, computing the magnetic susceptibility and the Drude weight. This latter quantity presents a sudden variation as the spin-flop to paramagnet phase transition line is crossed. This effect could be used as a possible source of large magneto-resistance. Our findings may have some relevance for doped La_{2-\delta}Sr_{\delta}CuO_4 in a magnetic field.